1. Field of the Invention
This invention relates to a powder filling method in which powder is filled in a powder box, thereafter the powder is moved over a cavity arranged at a die plate and the powder is dropped into the cavity by its gravitational force.
2. Description of the Related Art
In the case of manufacturing a metallic sintered component parts, for example, in the prior art, raw material powder attained by mixing various kinds of metallic powder represented by iron powder with lubricant agent or the like is filled in the cavity (a molding die) to perform its molding operation, thereafter the molded product is put into a furnace for performing a sintering operation. When the raw material powder is filled in the cavity, there is provided usually a method, as shown in FIG. 1 in which the powder 3 is filled in advance in the powder box 1 having a discharging port 2 opened at its bottom segment and set over a die plate 4, the powder box 1 is fixed to the extremity end of the rod 6, the powder box is slid on the die plate 4 at a specified speed by a driving mechanism such as a hydraulic cylinder (not shown), the powder 3 in the powder box 1 is dropped into the cavity 5 to be targeted by its own gravitational force through the discharging port 2.
However, when the powder 3 is filled from the powder box 1 into the cavity in this way, the system having a complex shape of the cavity 5 or poor filling characteristic or poor flowing characteristic in reference to the type of powder produces a poor filling of the powder into the cavity 5 or disturbance in particle size or substances and the like, resulting in that this state becomes one of the causes of poor quality.
As means for solving such problems, there have been proposed, in the prior art, one method for filling powder while a moving speed of the powder box is being decreased and the other method for filling the powder by flowing out gas through some fine holes in a pipe installed in the powder box while the powder is being floated.
Although the former method could not attain an improvement of filling rate as expected to cause its productivity to be decreased and the latter method was expected to have a substantial effect for improving the filling rate and the like, these prior art methods had some problems that their structures were complex and it was necessary to perform a precise control over supplying of gas, and so it could not say that they were sufficient methods.
Further, as already disclosed in JP-A No. 300,194/1996, although there has been proposed a method for mounting a reciprocatable fork in the powder box, this prior art merely provided an effect for scraping off the bridge formed in the powder box and dropping it, so that it showed a certain limitation in improvement of the filling rate and so this prior art method was not a sufficient method.
This invention has been invented as its subject matter to overcome the aforesaid prior art problems, drop the powder positively into the powder box by a simple constitution and means without damaging its productivity and improve the filling rate.
In order to improve some problems in the prior art described above, the present inventors have earnestly performed various kinds of experiment and studies and finally completed the present invention as the advantageous solving means for overcoming the aforesaid problems.
According to one aspect of the present invention, there is provided a powder filling method in which powder is filled in a powder box having a discharging port at its bottom segment, the powder box is moved over a cavity to be targeted while being slid on a die plate, thereafter the powder in the powder box is dropped into the cavity by its own gravitational force and filled there, wherein when the powder in the powder box is at least dropped into the cavity, the powder in the powder box is applied with a rotary agitation.
According to another aspect of the present invention, there is provided a powder filling method in which the rotary agitation is performed by a mechanical rotary agitation.
According to another aspect of the present invention, there is provided a powder filling method in which the rotary agitation is performed by a mechanical rotary agitation with its substantial vertical direction being applied as a rotating axis.
According to still another aspect of the present invention, there is provided a powder filling apparatus comprising a powder box movably arranged over a die plate; a motor arranged at the powder box; and a rotary agitating machine arranged in the powder box and rotated through driving of the motor with a substantial vertical direction being applied as an axis.
According to yet another aspect of the present invention, there is provided a powder filling apparatus in which the rotary agitating machine has a plurality of agitating rods.